Tracked amphibian vehicles were developed prior to World War II and saw much use in the Pacific Theater as an amphibious assault craft that could go ashore and operate on land. Wheeled amphibians such as the “Duck” were also employed in WW II. Those vehicles usually used propellers to help the tracks and wheels on the water and were very slow, with water-speeds less than 10 mph. At the end of the 20th century there were still no operational military vehicles that could better the 10 mph water-speed. Snowmobiles with their rubber tracks had been running over the water at high speeds for over 25 years. However, a snowmobile cannot slow down below planing speed or it will sink and it cannot start or stop in the water. Large ships can operate at high speeds without planning because of their large size and the hydrodynamic scaling effects. Small boats, however, can only achieve high speeds efficiently by planing.
At the end of the 20th century, the US Navy started the development of a tracked amphibian for the Marine Corps that could get over the hump (the speed at which planing starts) and on to the plane. This vehicle, now called the Expeditionary Fighting Vehicle (EFV), can carry 20 men and weighs 74,500 lbs. It is capable of 29 mph on the water. It is a tracked vehicle that retracts its tracks, folds planing boards out and under the tracks, and uses two large water jets for propulsion on the water. The dual propulsion system of tracks and water jets increases the complexity, cost, weight and maintenance. Introduction of the EFV into military service is dependent on a successful solution of the shortcomings of the production model.
Recently, even higher water-speeds have been achieved with several different experimental amphibious automobiles in the USA and abroad. They retract their wheels, fold out boards under the wheels and use either propellers or water jets for propulsion. Here again they have added complexity because of the dual propulsion system of wheels and water jets, and the wheels, of course, do not provide the all terrain capability of tracks for operating in deep mud, snow, sand, ice, and marshes.